1. Field of the Invention
The present invention relates to a liquid crystal display device of negative display type having a light shielding layer formed therein.
2. Discussion of Background
Heretofore, a negative display wherein characters or patterns are displayed brightly on a dark display surface has been used in many cases for liquid crystal display devices used for the display portions of watches or meters for automobiles.
In a negative liquid crystal display device, no voltage is applied to the liquid crystal layer at the background area other than a display area and liquid crystal molecules are twisted at the background area, whereby light propagates along the twisted liquid crystal molecules, and a pair of polarizing films are disposed with their polarization axes being in parallel with each other so that no light is transmitted at the background area.
However, the negative liquid crystal display device had a problem that polarization efficiency reduces when light propagates in a twisted fashion, light having a certain color is transmitted to some extent, whereby there is caused insufficient contrast at the background area.
In order to resolve the above-mentioned problems, it has been proposed to form a light shielding layer at the background area other than a display portion.
In many cases, the light shielding layer is formed inside the cell in order to avoid such a phenomenon that the display pattern is deviated from the pattern of the light shielding layer when seen from an oblique direction.
When the light shielding layer is made of a metallic film, the thickness of the layer can be small and a high light shielding properties can be obtained. However, since the metallic film has electric conductivity, it is necessary to provide a complete insulation means between the electrodes and the light shielding layer so as not to cause short-circuitting between the electrodes. However, it is difficult to obtain a thin insulating layer having a large surface area without any pin-hole, and there is a possibility of short-circuitting between neighboring electrodes. In order to eliminate the above-mentioned problem, there has been known to form a light shielding layer of a thick film by a printing method or the like. In this case, there is no risk of short-circuitting between the neighboring electrodes even by using ink in which electric conductive particles such as carbon are used as a pigment. However, the thickness in average of the light shielding layer is large such as 2 .mu.m-5 .mu.m. Accordingly, a problem of short-circuitting between the substrates arises. In order to eliminate such disadvantage, use of ink including a non-conductive pigment is proposed.
Use of the ink including the non-conductive pigment reduces the problem of short-circuitting between the neighboring electrodes and between the substrates. However, when a light shielding layer was formed at the background area with use of the ink including the non-conductive pigment to thereby obtain high light shielding function, it was necessary to form a thicker light shielding layer in comparision with the case that the light shielding layer was formed by using ink in which electric conductive particles such as carbon particles are used as the pigment. In this case, it is difficult to provide a uniform cell gap, and unevenness of color or misalignment of the substrates apt to occur. Further, a part of the cell gap is extremely narrowed, and the liquid crystal can not smoothly introduced into the cell.